In recent years, operators focus on an Internet Protocol Television (Internet Protocol Television, IPTV for short) service, in which a set top box together with a television serves as a terminal, a broadband IP serves as a transmission technology, and the service is centered on an audio-visual service and integrates instant communications, games and information services into a whole. From the second half of 2004, the national operators accelerate the pace of IPTV pilot construction. As an emerging service providing manner, the IPTV provides potential opportunities of new services, new income and new business modes, which may bring new profit growth to the communication and media service providers.
A live broadcast service as an IPTV basic service is the inheritance of the conventional television service, and quality of service of the live broadcast service should be at least equivalent to that of the existing cable television to ensure competitiveness of the IPTV. Therefore, the ensuring the quality of service (Quality of Service, QoS for short) of the live broadcast service is crucial to the smooth development of the IPTV services.
The packet loss or packet error may occur during transmission over the IP network. Forward Error Correction (Forward Error Correction, FEC for short) and Auto Repeat Request (Auto Repeat Request, ARQ for short) technologies are two common methods in the IPTV services to recover an original packet, and may also be used to ensure the QoS of the live broadcast service. The FEC technology is easily implemented, but needs to consume more redundant bandwidth, and moreover cannot recover the packet when being beyond the error correction capability. Therefore, in the actual application and standard organizations, the ARQ manner is usually used to recover the lost or error packet.
In the ARQ manner, a terminal receives multicast packet data corresponding to the live broadcast service, decodes the data and then outputs it, and in the receiving process, the terminal further detects whether the packet loss or error occurs according to a packet loss detection algorithm. If the packet loss or error occurs, a Nack message for request for data retransmission is directly sent to a retransmission server, and after receiving the Nack retransmission request, the retransmission server retransmits a designated packet to the terminal according to the instruction of the Nack message.
Through the method, the retransmission request of each terminal may be quickly fed back to the retransmission server. However, if the packet loss is not caused by the user side but occurs in an aggregation layer or a core node layer of the transmission network, every user can sense the packet loss. In such a case, the retransmission server may receive the Nack retransmission requests sent from multiple terminals almost at the same time (this condition is referred to as a Nack storm). The Nack storm in a short period may result in the following two problems:
1. A load of the retransmission server is increased instantly, which may possibly cause the abnormal working state or cause that the retransmission requests of some terminals cannot be responded timely.
2. Data packets are retransmitted to multiple users at the same time, which causes that the occupied network bandwidth is increased sharply. As a result, it is difficult to plan the network bandwidth, network congestion may be possibly caused, the packet loss is further intensified, and the whole system is caused to be in an unstable state.